Yin and Yang are concepts of dualism used to describe how apparently opposite or contrary forces are actually complementary and interconnected in the natural world. Yin and yang are always opposite and equal qualities. Everything has both yin and yang aspects (for instance shadow cannot exist without light). Whenever one quality reaches its peak, it will naturally begin to transform into the opposite quality: for example, grain that reaches its full height in summer (fully yang) will produce seeds and die back in winter (fully yin) in an endless cycle.